Electronic imaging cameras for recording still images are well known in the art. Such cameras can record a plurality of still images on a single magnetic disk or tape in either analog or digital format for subsequent playback on any well-known cathode ray tube viewing device. Printers may also be utilized with such cameras in a well-known manner to provide hard copy of the recorded images. Such electronic imaging still cameras may utilize two-dimensional image sensing arrays such as charge coupled devices (CCD's) which integrate incident scene light over a predetermined time to provide an electronic information signal corresponding to the scene light intensity incident on the array. Such two-dimensional image sensing arrays comprise a predetermined number of discrete image sensing elements or pixels arranged in a two-dimensional array in which each image sensing element responds to incident illumination to provide an electronic information signal corresponding to the intensity of the incident illumination.
In order to record color images, the illumination incident on the two-dimensional image sensing array is filtered so that different image sensing elements receive different colored illumination. The filters are arranged in well-known patterns across the face of the image sensing array, such as a repeating pattern of red, green and blue stripes. Alternatively, individual image sensing elements or pixels across each line may be filtered in a repeating pattern of red, green, blue, green filters, as is well known in the art. Since each image sensing element can only detect one color of illumination, the color information for the other colors not detected by that image sensing element must be filled in. Filling in the missing color information is generally accomplished by interpolating the detected image data for each color to determine color values for all the colors for each image sensing element. In particular, there results three groups of image sensing elements of which respective ones have measured values for one given color and an interpolated value for the other two colors.
Conventional types of interpolation, however, can provide images with objectionable aliasing artifacts such as "color fringes" near sharp edges. The conventional approach to solve this problem is to eliminate the color fringes at the expense of image sharpness by either blurring the picture or removing selected spacial frequencies from the picture (antialiasing) so that edges do not create color fringes. Blurring the image in this manner, however, has its obvious disadvantages resulting in a reduction in resolution and a so-called "fuzzy" picture.
In my earlier U.S. Pat. No. 4,663,655, which issued on May 5, 1987, there is described a novel technique for providing the desired interpolated values. In this technique, there is first inserted for the missing values approximate values derived by simple linear interpolation in the usual fashion, and thereafter, the resulting values are used to derive a number of difference values for each of the pixels by subtracting the resulting values at different pairs of colors. These difference values are then passed through a simple linear median filter to reduce the color fringe artifacts described above, and then the various filtered differences are combined to reconstruct three color values at each pixel for use in the image scene reproduction.
While this technique provides a considerable improvement, each color image signal processed requires a separate median filter of a relatively complex nature.
Accordingly, it is desirable to eliminate color fringing artifacts in the aforementioned manner using fewer median filters of a less complex nature.